Water treating method



Patented Oct. 19, 1943 OFFICE WATER TREATING METHOD Melvin A. Enquist, Houston, Tex.

N o Drawing. Application August 11, 1941; Serial No. 405,403

9 Claims. (Cl. 252 -387) This invention relates generally to a water treating method, and more particularly to treating waters and aqueous solutions to inhibit the corrosion of metals in contact with these liquids.

This application is a continuation, in part, of application Serial No. 303,796 for a Water treating compound and method, filed by applicant on November 10, 1939.

Water and aqueous solutions are used industrially as cooling and heating media and as antifreezes, and their use is sometimes expensive because of the corrosive action they exert on the metals with which they are in contact. As an exampleice is manufactured by circulating an aqueous solution of either calcium chloride or sodium chloride at a low temperature around cans containing water. The aqueous solution or brine is below the freezing temperature of water and absorbs heat from the water, freezing it. The presence of calcium or sodium chloride in the brine permits the carrying of a low temperature in the brine without freezing it, but freezing the water in the cans. The presence of the chlorides increases the conductivity of the brine. and makes the brine corrosive, attacking the iron cans, or zinc coated cans, and piping. As another example-water is commonly used as a coolant in engine jackets. Because of the natural salts present in the water it attacks the iron piping and water jacket, resulting in severe corrosion.

The term aqueous solutions is used to designate those water solutions of compounds such as sodium chloride, calcium chloride, ethyl alcohol, and ethylene glycol, or other compounds dissolved in water, used industrially in the transfer of heat, generation of power, and prevention of freezing. It does not apply to those chemical solutions used in chemical process manufacture, such as acid solutions, used for the preparation of acids or other salts or compounds.

The treatment of these waters and aqueous solutions is desirable where this corrosion exists. A metal is corroded because of its failure to provide itself with a protective coating, and because of the formation of varying potentials on its surface. It is desirable, therefore, to introduce into the solution a compound that will form an adherent protective coatin on the metal, or a compound that will form a partial adherent coating on the low potential parts of the metal. Phosphates are known to reduce the corrosion rate of a metal by the formation of a protective phosphate coating on the metal. This coating is not is not adherent nor does it prevent anodic corrosion, or corrosion formed by varying potentials.

This invention relates to a chemical compound that will produce an adherent coating on a corrosive metal in a water or aqueous solution, and in some cases produces a partial protective coating, preventing anodic corrosion.

The invention comprehends a method of producing a water soluble polyphosphate compound, comprising. at least one polyphosphate radical, an alkali metal cation, and a normally solid element, other than phosphorous, of groups II to VIII as listed in the periodic table including copper from Group I, having a normally solid oxide and comprisin part of said cation.

This series of compounds is prepared by the fusion of an alkali acid phosphate with a normally solid oxide, or combinations of the alkali acid phosphate and di alkali acid phosphate with a normally solid oxide. The proper percentages of phosphate and oxide must, of course, be used.

The alkali metals may be defined as potassium, sodium, lithium, and include the ammonium radicals as equivalent of the alkali metals and are generally effective, as in many cases the coating contemplated as suitable material.

The probable theoretical explanation of this series of compounds is: An'element with a. greater solution pressure tends to cause the deposition of an element of less solution pressure when placed in a solution of its salt. Thus, when iron is exposed to a water containing a small percentage of sodium copper phosphate, a copper plating is formed on the iron, inhibiting further corrosion. This plating consists almost wholly of copper, with a slight amount of copper phosphate, and is adherent and protective.

When iron is exposed to a solution containing sodium zinc polyphosphate, a partial but protective coating is formed on the iron surface, consisting of zinc and the phosphate radical.

The action of these compounds may be described in this manner:

When a metal is exposed to a solution containing a small percentage of an alkali element phosphate, and the element in combination with the phosphate is cathodic to the metal exposed, the metal, because of its greater solution pressure, displaces the element from the salt, and the element coats the surface of'the metal. When the alkali phosphate is in combination with an element anodic to the metal exposed. a base exchange takes place and the metal forms a partial coating of the element phosphate.

In preparing these compounds it is preferable to use the proper proportions of sodium or p0,-

tassium acid phosphate and the element oxide and fuse the mixture. Another method is to use percentages of sodium or potassium acid phosphate and disodium or dipotassium phosphate and the element oxide and fuse the mixture. The equivalent of the oxide may be used, as example, calcium carbonate may be used in place of calcium oxide.

In order to illustrate the principles of my invention, a number of specific examples are hereinafter given. However, it should be distinctly understood that I do not confine myself to the specific treating agents, proportions, temperatures, time intervals, testing procedures, or aqueous solutions hereinafter disclosed, as it should be understood by those skilled in the art that variations from these disclosures do not depart from the principles and spirit of my invention which is directed in a general way to the use of complex polyphosphate compounds of the type herein described in the treatment of aqueous solutions to prevent corrosion and pitting of base metals in contact with said solutions.

I have found it preferable to prepare these alkali metal polyphosphate compounds by using definite ratios of the phosphorous content of the alkali phosphate to the valence of the metal in the form of metal oxide. As an example: Six phosphorous elements in the form of sodium dihydrogen phosphate will combine with four valences of metal. Given below are several examples illustrating this principle.

Example 1.-Six molecular weights of sodium dihydrogen phosphate are mixed with two molecular weights of zinc oxide in the powder form, and the mixture placed in a furnace and fused until a clear glass fusion product is obtained, and this fusion product is cooled. The rate of cooling should be the normal rate of a small quantity exposed to the atmosphere temperature, or the cooling rate may be said to be rapid. The resultant compound is colorless and water soluble.

Example 2.--A sodium copper polyphosphate may be prepared in the same manner. Six molecular weights of sodium dihydrogen phosphate combine with two molecular weights of copper oxide. Proportional weights of these two compounds in the powder form are mixed. and the mixture placed in a furnace and fused until a clear green glass fusion product is obtained, and this fusion product is cooled at a rapid rate. The resultant compound is green and water soluble.

Example 3.-A sodium calcium polyphosphate may be -prepared in the same manner. Six molecular weights of sodium dihydrogen phosphate combine with two molecular weights of calcium oxide. Proportional weights of these two compounds in the powder form are mixed, and the mixture placed in a furnace and fused until a clear glass fusion product is obtained, and this fusion product is cooled at a rapid rate. The resultant compound is colorless and water soluble.

Those polyphosphate compounds described in Examples 1 to 3 may be designated as sodium (metal) poly metaphosphate.

Example 4.-The alkali metal polyphosphates may be prepared also by the use of dialkali hydrogen and the monoalkali phosphates with the metal oxide. These compounds may be desi nated as sodium (metal) poly pyrophosphates.

Example 5.-Two molecular weights of mono sodium ortho phosphate, and one molecular weight of disodium orthophosphate and one molecular weight of zinc oxide. mixed in the powder form and fused to a molten state or until a clear glass product is obtained, and cooled at a rapid rate, results in a water soluble compound. Examples of the usage of this material are: A water having the following composition:

P. P. M. Sodium chloride 300 Sodium bicarbonate 150 Calcium, bicarbonate 30 was found to corrode samples ofiron at the rate of 30 milligrams per square decimeter per day, when the iron was .fully immersed in the water, and the water allowed to saturate itself with oxygen. The temperature of the water was maintained at degrees Farenheit. Various sodium metal polyphosphates were introduced into samples of this water and the weight losses of iron samples exposed to these treated water samples were determined. The concentration of the polyphosphates was 2#s per 1000 gallons of water. Weight losses were:

Sodium zinc poly metaphosphate 4.9 Sodium zinc polypyrophosphate 5.4 Sodium calcium polymetaphosphate 8.6 Sodium copper polymetaphosphate 15.4

Brines are very corrosive and this chemical was introduced into a solution of sodium chloride (20% by weight) in the proportion of 2#s per gallons of brine. Normal weight loss in an untreated brine is in the order of 15 to 20 mg./sq. dm./day. Sodium zinc metapolyphosphate in the proportion of 2#s M gallons reduced the corrosion rate to 0 mg./sq. dm./day. Actually the sample of iron recorded an increase in weight due to formation of a zinc phosphate coating.

The proper concentration of these compounds in solutions to prevent or inhibit corrosion varies with the chemical content of the solution and the surface of metal exposed. Generally 1#s of the alkali metal polyphosphate per 1000 gallons of solution effectively inhibits corrosion. The effective limits may be said to be from A# per 1000 gallons to 10#s per 1000 gallons or the maximum solubility of the salt.

The term water-soluble as used herein and in the appended claims is also descriptive of the very slight solubility exhibited by certain of these polyphosphate complexes whose solubility, however, is sufficient to allow the plating out" and base exchange reactions hereinabove described.

The term polyphosphate complex as used herein and in the appended claims is descriptive of various polymeric and condensed forms of phosphate, all of which are generically derived by molecular dehydration of ortho-phosphoric acid compounds, and which are further characterized by the presence of at least one polyvalent metallic ion or radical derived from a normally solid metallic oxide other than phosphorus.

The term phosphoric acid compounds" refers to the acids and salts of the various phosphoric acids, including ortho, meta, pyro, tetra, etc.

The term alkali metal equivalent refers to sodium, potassium, lithium, or their hydrogen or ammonium equivalents. For instance, a polyphosphate compound may have one or more hydrogen atoms or one or more ammonium radicals in place of sodium, since all of these are monovalent ions or radicals.

Although preferred embodiments of the invention have been described and the preferred manner of practicing the invention disclosed, and the probable theories given to explain the actions involved in the invention, it will be understood that it is not limited thereto, but may be otherwise embodied, and practiced, within the scope of the appended claims.

What I claim is:

1. A method of inhibiting Or preventing the terized by its ability to form a protective film on metals basic to hydrogen.

2. A method of inhibiting or preventing the corrosion of base metals in aqueoussolutions of the type described, comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble poly-metaphosphate complex of the type formula,

wherein A is an alkali metal equivalent, M is a polyvalent metal ion derived from a normally solid metallic oxide other than phosphorus, Pc03x+l is the polybasic polyphosphate radical, n represents the number 1 or more, and 11. may be 1 or more, and with the additional proviso that the sum of the valences of n+n' shall not exceed the I sum of :r+2, and a: is 2 or more.

4. A method of inhibiting or preventing the corrosion of base metals the type herein described comprising adding to such solution a corrosion-inhibiting compound in aqueous solutions of complex characterized by the presence of at least one metaphosphate radical, at least one alkali metal equivalent, and at least one polyvalent me-.

tallic radical derived from a zinc oxide.

5. A method of inhibiting or preventing the corrosion of base metals inaqueous solutions of the type herein described comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble poly-metaphosphate complex characterized by the presence of at least one metaphosphate radical, at least one alkali metal equivalent, and at least one polyvalent metallic radical derived from a manganese oxide.

6. A method of inhibiting or preventing the corrosion of base metals in aqueous solutions of the type herein described comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble poly-metaphosphate complex characterized by the presence of at least one metaphosphate radical, at least one alkali'metal equivalent, and'at least'one polyvalent metallic radical derived from a copper oxide.

7. A method of inhibiting or preventing the corrosion of base metals in aqueous solutions of the type herein described comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble polybasic polyphosphoric acid compound characterized by the presence of at least one polybasic polyphosphoric acid radical.

at least one alkali metal equivalent, and at least one polyvalent metallic radical derived from a zinc oxide.

8. A method of inhibiting or preventing the ,corrosion of base metals in aqueous solutions or the type herein described comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble polybasic polyphosphoric acid compound characterized by the'presence of at least one polybasic polyphosphoric acid radical, at least one alkali metal equivalent, and at least one polyvalent metallic radical derived from a manganese oxide.

9. A method oi! inhibiting or preventing the corrosion of base metals in aqueous solutions 0! the type herein described comprising adding to such solution a corrosion-inhibiting compound comprising a water-soluble polybasic polyphosphoric acid compound characterized by the presence of at least one polybasic polyphosphoric acid radical, at least one alkali metal equivalent. and at least one polyvalent metallic radical derived from a copper oxide.

, MELVIN A. ENQUIS'I'.

comprising a water-soluble poly-metaphosphate A 

